Instead of taking an arbitrary amount of T3 and T4, it would be wise to address potential dietary deficiencies and autoimmune triggers first and foremost.
However, if exogenous T3 and T4 use is something you are dead set on, or you already use one or the other, you would benefit from knowing what healthy endogenous production actually equates to.
I often see in the bodybuilding community this idea that 25 micrograms is not even a replacement dose for your natural T3 production.
In a fat loss context, many bodybuilders assume that you need significantly more than that to produce appreciable fat loss.
This is all misguided information and should be clarified with closer examination.
Healthy T3 And T4 Production
On average, those with a healthy functioning thyroid gland secrete between 10-22 micrograms T3 and 94-110 micrograms T4 daily [R].
1 grain of natural desiccated thyroid (NDT) is approximately 9 mcg of T3 and 38 mcg of T4.
On paper, healthy endogenous secretion equates to approximately 3 grains NDT.
However, some individuals with hypothyroidism may need more than that to achieve optimal results.
T3 and T4 Reference Range
Thyroid hormone production is much like testosterone in that there is a reference range.
When you look at testosterone levels (free testosterone and total testosterone), the reference ranges are VERY general, which I'm sure you're aware of.
The reference range can be as low as 250 ng/dL, upwards of 950 ng/dL for total testosterone.
Some labs even go as high as 1100+ ng/dL.
When it comes to T3 and T4, there is a reference range as well, which is what is generally viewed as “healthy”.
I think it goes without saying that a level on the low end of healthy function is not going to yield the same quality of life in many cases as a level closer to the middle, or on the high end of normal.
With that being said, oral absorption of exogenous thyroid hormones will not equate to exactly what your body would produce endogenously with healthy natural function.
For example, popping a 25 mcg pill of Cytomel does not mean that you are directly supplying your tissues with 25 mcg after your body has broken that pill down.
However, using clinical data as a reference point for where exogenous thyroid dosages should start is helpful.
If euthyroid humans secrete 10-22 micrograms of T3 and 94-110 micrograms of T4, logically you can assume that you will probably need at least that much exogenous T3 and T4 to build up adequate serum concentrations in the blood.
This is where many individuals run into problems though, as they will often start off the bat at 25 mcg+ of Cytomel monotherapy.
Aside from the various potential issues that arise via traditional monotherapy, this dosage could be too high off the bat for many individuals.
The same sort of thing happens in the bodybuilding community all the time with testosterone replacement therapy.
Some bodybuilders will say that they are healthy and only using “TRT”, when the reality is that they are injecting 250 milligrams per week, which is actually the equivalent of being on a mini cycle year round.
Addressing The Root Of Hypothyroidism
It isn't normal for your body's immune system to attack and destroy your thyroid gland.
It is triggered by something, and oftentimes the issue comes down to autoimmune problems.
The most common triggers of thyroid issues are dietary deficiencies, ingesting things that your body simply can't handle, and environmental factors that are not being accounted for.
Micronutrient deficiencies can result in suboptimal T4 production, as well as inhibit your body from converting T4 to T3 efficiently.
Sometimes hypothyroidism is as simple as a Selenium deficiency caused by a subpar diet.
If hypothyroidism is brought on via an autoimmune disorder, this gets a bit more complicated as there are many autoimmune triggers that can be the root of the issue.
Things like medications (even the fillers in the medications), stress, viral infections, environmental toxins, compromised gut health (like leaky gut), and food sensitivities can all trigger an autoimmune flare where your body starts attacking your thyroid gland.
Now, while some individuals have complex issues that aren't easily addressed, in general, if the thyroid gland hasn't been destroyed by the immune system, autoimmune flares can be attenuated in most cases simply by deploying a well constructed fasting protocol and/or elimination diet where you start to pull out any food groups (and things you ingest in general) that could be triggering your autoimmune flare.
For some, removing gluten or dairy is all it takes.
For those with extremely compromised gut health, removing literally everything except 1 or 2 food groups that supply the body with a sufficient amount of macronutrients and micronutrients may be necessary.
It all depends on your current situation and state of gut health.
Mikhaila Peterson is an extreme example of this, and her story just goes to show how a “healthy” diet on paper may actually be harmful to you if you have intolerances to the foods you are ingesting.
This is one reason why some individuals with thyroid issues can experience temporary relief with medications, and then suddenly experience a massive downward spiral down the line while using the exact same medication.
Just because you're supplying tissues with a certain amount of thyroid hormones via exogenous NDT, you are not addressing the root of your issue which is destroying your body in the first place.
If you have an autoimmune disease, your priority should be fixing that before your body destroys itself, not throwing a bandaid over it with T3 and T4 and then assuming you are fine and can continue with the exact same diet and lifestyle.
If your body is attacking itself, it is telling you something.
It is telling you that your current lifestyle, environment, and/or diet is not healthy for you.
If you figure this out early enough, you can identify the problem, address the root cause of it, and maximize your likelihood of getting healthy again rather than slapping a bandaid on it with exogenous T3 and T4.
Now, this isn't to say that T3 and T4 should never be used, but obviously the ideal scenario would be that you heal your body naturally as the autoimmune disease is not going to just randomly stop if the triggers have not been removed.
Recovering Healthy Thyroid Function Vs Hormone Replacement Therapy
When comparing the hypothalamic–pituitary–thyroid axis relative to the hypothalamic–pituitary–gonadal axis it becomes apparent that the Thyroid is more elastic in its ability to recover, even after significant bouts of functional suppression.
The thyroid seems to bounce back much more easily than natural testosterone production does after endogenous suppression.
This is not to be confused with autoimmune disorders that literally destroy the gland itself.
I'm referring to endogenous hormone suppression caused by using exogenous thyroid hormones (hypothalamic–pituitary–thyroid axis) or testosterone (hypothalamic–pituitary–gonadal axis).
Even after abusing T3 for years my thyroid still bounced back.
I was afraid to come off as I thought that my thyroid production would stay crashed and I would gain tons of fat, but that wasn't the case.
Even after a full year of artificially inducing a state of hyperthyroidism, I recovered adequate thyroid function within weeks of discontinuing T3.
That's something that's probably not going to happen with natural testosterone production after several years of abuse of exogenous androgens though.
Now, I'm not trying to say that hormone recovery is impossible after blasting steroids, however, I am trying to highlight the fact that when it comes to thyroid hormone production, it is typically much easier to recover healthy endogenous production, and it is worth trying to get back to a healthy level naturally even after years of abuse.
Misconceptions About Using T3 And T4 For Fat Loss
When I was completely enamored with bodybuilding years ago I noticed that anytime I used more than 50 mcg T3, regardless of what steroids I was running concurrently, I would start flattening out and lose muscle.
Be cautious of this, as I do not see any significant benefit to pushing yourself into hyperthyroid range unless you're competing in a bodybuilding show and you absolutely need to lose insane amounts of body fat.
And even then, if you need to artificially induce hyperthyroidism levels of T3 to lose enough fat before an event, you probably didn't allocate yourself enough time to diet down in the first place.
When it comes to T3 and T4, I don't think it's something that really needs to be pushed during a cutting phase.
Don't get me wrong, it helps, but T3 is the most catabolic fat burner you can use, even in the presence of exogenous androgens.
It's common for newbies to use upwards of 75-100 mcg T3 for a cutting phase.
Many of the top pros nowadays minimize their T3 use because of how badly it flattens you out and how catabolic it is at higher dosages.